This may sound easy but it isn't. A lot of people choose with their eyes which is great if you want to have a really good looking collection but choosing a healing Crystal is different. It has to have the right vibration. Here is a step by step guide to choosing the correct Crystal for you.
1) Choose two or three pieces that catch your eye first...
2) Hold each of the chosen stones seperately for two or three minutes...
3) You may feel a tingling sensation whilst holding the stone, it will feel as if the stone is buzzing in your hand...
4) Doing the same with the other stones discard the ones that don't feel the strongest to you.
If this does not work for you then go with your instinct...that maybe by sight or just the feel of the stone. If it feels right to you then that is the one you want.